1. Field of the Invention
The present invention relates to a liquid crystal display device in which blue light is used in a backlight and particularly to a liquid crystal display device in which the use efficiency of blue light from the backlight is increased and color reproducibility and brightness are improved.
2. Description of the Related Art
Liquid crystal display devices (hereinafter, also referred to as LCDs) have been used in a range that broadens every year as low-power consumption and space-saving image display devices. Liquid crystal display devices have a constitution in which a backlight (hereinafter, also referred to as BL), a backlight-side polarizing plate, a liquid crystal cell, a display-side polarizing plate, and the like are provided in this order.
Recently, for liquid crystal display devices, development for power saving, high definition, and color reproducibility improvement has been progressing in order to improve LCD performance At the moment, the demand for power saving, high definition, and color reproducibility improvement is intense for small-size devices such as table PCs and smartphones; however, even for large-size devices, development for next-generation high-definition televisions (4K2K, European Broadcasting Union (EBU) ratio of 100% or higher) of the current TV standards (FHD, National Television System Committee (NTSC) ratio of 72%≈EBU ratio of 100%) is progressing. Therefore, there is an intensifying demand for power saving, high definition, and color reproducibility improvement in liquid crystal display devices.
In order to increase the light use efficiency in response to the power saving of backlights, there are cases in which an optical sheet member is provided between a backlight and a backlight-side polarizing plate. The optical sheet member refers to an optical element that, out of incident light rays vibrating in all directions, only transmits light rays vibrating in a specific polarization direction and reflects light rays vibrating in the other polarization directions. As a core component of low-power LCDs which are widely used in accordance with the broad distribution of mobile devices and a decrease in the power consumption of home appliances, the optical sheet member is expected to solve the low light use efficiency of LCDs and thus increase brightness (the degree of the brightness of a light source per unit area).
Regarding the above-described optical sheet member, a technique in which a specific optical sheet member, for example, a dual brightness enhancement film (DBEF) or the like is provided between a backlight and a backlight-side polarizing plate, thereby improving the light use efficiency of the BL by means of light recycling and improving the brightness while saving the power of the backlight is known (refer to JP1997-506984A (JP-H09-506984A)). Similarly, JP1989-133003A (JP-H01-133003A) describes a polarizing plate having a constitution in which a λ/4 plate and a cholesteric liquid crystal phase are laminated together. When the bandwidth is broadened using a layer obtained by fixing three or more cholesteric liquid crystal phases in which the pitches of the cholesteric phases are different from each other, it is possible to improve the light use efficiency of the BL by means of light recycling. However, the above-described optical sheet member has a complex member constitution, and thus, in order to distribute the optical sheet member in the market, it has become essential to reduce the costs by decreasing the number of members by means of the additional function integration among the members.
In addition, in a display system of JP2014-502403A, an optical active structure including nanorods is irradiated with short-wavelength unpolarized light (wavelength λ0) ejected from a pumping light source, and thus the optical active structure ejects polarized light having a color gamut necessary for display devices (for example, wavelengths λ1, 80 2, and λ3). The polarized light ejected from the structure passes through an optical polarizer, then, passes through a liquid crystal structure, and passes through a polarizer. A liquid crystal panel can be disposed between two glass plates capable of including an RGB filter and a polarizer (not illustrated) attached to the RGB filter. A polarization state having a higher degree of polarization can be obtained using a polarizer. In addition, in the display system, one or more optical elements such as diffusers, brightness enhancement films (BEFs) or dual brightness enhancement films (DBEFs) are provided, the diffusers make the optical distribution spatially uniform, and, in a case in which the diffusers are directly optically attached to the structure, the diffusers aid light extraction from the structure. When light is reused using a brightness enhancement film and a dual brightness enhancement film, brightness can be improved.